Reversal development of light-sensitive silver halide emulsions



mama May 23, 1939 BEVERSAL DEVELOPMENT OF LIGHT-SEN- SITIVE SILVER HALIDE EMULSIONS Gustav Wllmannl, Wolfen, Kreil Bitterfeld, Wilhelm Schneider, Desaan',

Bitterield, signments, to

and Richard Kethnr,

Germany, assignorl, by mesne as- Agfa Ansco Corporation, Bingbamton, N. Y., a corporation of Delaware N'o Drawing. Application October 29, 1937, Se-

mi No. 111.102. 1930 Our presentinvention relates to reversal de- Lelopment of light sensitive silver halide emulons.

It is known that the reversal development of '5 light-sensitive silver halide emulsion layers may be carried out without intermediate exposure to light if thenegative silver image is removed in the second development by means of an alkaline developer containing a small proportion of an 10 odorless sulfur compound, especially thiosinamine. It has also been proposed to use this sulfur compound not in the developing bath but in an intermediate bath or in a clearing bath containing suliite. These baths containing the sulfur compound have, however, certain disadvantages. In consequence of the-instability of the sulfur compounds, for example thiourea derivatives, abundant quantities of silver sulfide sepa- "ratein the bath whether it beneutral or alkal line. The silver'suliide. produces, particularly in the colloid form, brown tints and is not bleached I by the usual reducersuch as mercuric chloride or potassium ferricyanide used for the purpose. The reversal development with the aid of sulas fur compounds in neutral or alkaline solution is in particular little suitable for use in making multi-color pictures because in consequence of the strong blackening of the picture by the separation of black silver sulfide no useful result can so be attained.

It is an object of the present invention to avoid or minimize these dimculties and disadvantages of tl'iehitherto known reversal process.

A further object is to provide a photographic s5 reversal process using'an intermediate bath with an odorless sulfur compound while preventing precipitation of silver sulfide.

A further object is the provisionof a process for developing multi-color pictures according to 40 the reversal method in' which process the undesirable blackening of the color tint of the multicolor pictures is avoided. a

Further objects will be apparent from the de-' tailed specification following hereafter.

(5 We have discovered that by using the sulfur compound in acid-solution .the sulfur compounds is quantitatively avoided so that the disturbing precipitation of silver sulfide is prevented and also the blackening of the color 50' tint; of the multi-color picture. These acid baths have further the great advantage of a much I longer duration than: the hitherto known neutral or alkaline baths. The nature of the acid used is without importance,'its pH-value being alone dees 'cisive. The sulfur compound may be used, for

the decomposition of In Germany November 10, s

2 Claims. (01.95-88) example, in a solution of acetic acid, oxalic acid,

citric acid, sulfuric acid or phosphoric acid.

Suitable odorless sulfur compounds for producing silver sulfide nuclei are, for example, thiourea and its derivatives, (thiosinamine), N, N-diethyl-N'-allyl thiourea, N-phenyl thiourea, N, N-diethanol-N'-phenyl thiourea. v

The process is suitable for the reversal development of any black-and-white or color, picture, especially for producing color reversal pictures which are produced by'color forming development. These latter are first developed in an ordinary negative developer, then treated in an acid bath containing a sulfur compound. which is odorless and can produce silver nuclei, and then developed .in a color developer to produce a positive. Silver halide emulsion layers containing dyestuff components which are fast to diflusion 'such as are described in U. S. patent applications Ser. No. 72.718, filed April 4, 1936; Ser. No. 90,728, filed July 15, 1936; Ser. No. 94,340, filed August 5, 1936; Ser. No.'158.860, filed August 13.

1937; Ser. No. 159,518, filed August 1'1, 193 andthe U. S. Patent applications Ser. No. flied September 18, 1937; and Ser. No. 166,832. filed October 1, 1937, may be developed by the process herein described.

tion:

A multi-layer photographicmaterial in which the layers contain dyestuff components fast to diifusion is. developed after exposure in one of the usual negative developers for example that known under. the registered trade-marks Amidol or Metol", and is then treated with an intermediate bath consisting .of 1000 cc. of water, 5 -cc. of glacial acetic acid and 0.4 gram of thiosinamine. It is then developed with a color developer, for instance N, N-dlethyl-para-phenylene diamine, washed and the silver image removed with Farmers Reducer, followed by further washing.

What we claim is: v

"In a process of developing a photographic silver halide emulsion by the reversal method, the improvement which comprises interposing between the'first and the second development an 'acid aqueous intermediate bath containing a thiourea capable of forming silver nuclei within said emulsion.

for instance N-allyl thiourea The following example illustrates the invenplurality of silver halide emulsion layers, each emulsion layers, developing said emulsion layers layer containing a color former fast to diffusion, with a developer capable of forming a dyestufi developing said photographic element by means image associated with a silver image, and removof a developer incapable of forming a dye with in: the residual silver from all the layers.

said color formers, treating said photographic GUSTAV WILMANNS. element in an acid aqueous bath containing a WILHELM SCHNEIDER. thiourea capable o'i' forming silver nuclei in said v RICHARD KE'I'HUR. 

